Maple glazing or case hardening?

Hi,

I'm clearly a newbie in woodturning, although I've had my lathe for over two years now. When I use a 1/4" bowl gouge on hard maple and take off a little wood at a time, the tip of my gouge gets really hot; so hot that I can feel the heat with my fingers 1-1.5 " away from the gouge tip. Can this heat cause the maple to glaze or possibly case harden and cause the surface to show darker and lighter "rings", particularly in the end grain areas and cause uneven absorbtion of a sealer like wax? Is hard maple more prone to this heat induced problem than other kinds of wood?

 

Your tool is dull so your having to push it into the wood. This causes excess friction. Dry wood often creates a lot of friction on it's own. combine the two and you get a lot of heat. Freshly sharpen your tool. then don't take as large of a bite. If necessary slow the speed of the lathe down. Between those 3 your tool should be cooler.

 

I'm a relative newbie at this as well and I have to think a dull tool is to blame. End grain will tear out or compress differently than side grain. Dull tools or inconsistent pressure against the wood will contribute to varying results. I've never observed glazing.

cg
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You're getting the rings? Heel bruises is what I think of. You're taking that "ride the bevel" business too much to heart. Most who do also consider that it means to lay the heel and toe on the surface. Mentally substitute "guide" for "ride" and leave some clearance angle as you work. You'll find you can guide parallel to the edge by controlling the bite and having a bit of skew into the direction of cut.

Can't tell how you're applying that bowl gouge to the wood from here, but presentation is more than half of apparent sharpness. If you get too high a pitch angle you don't sever cleanly. A lot of energy ahead of the edge goes into pushing the stuff up so you can cut it at all. Add that to useless heel drag and it means lots of friction, and therefore heat. Think of a razor or penknife. You can run your finger across the edge with no harm, but you don't dare run it along. That's how you want to present the tool - so the wood runs along the edge. Less work for you, the tool, and the lathe. Thus less friction and fatigue.

As to the heating and hardening, wipe the surface with a wet rag, let stand until what you pressed in is standing, and cut it off with sandpaper or a pass with a properly presented gouge, guided by the edge. If it's really bad, you might have to do it more than once.

 

I didn't address the rings. Many years ago Charles Alvis who was a former AAW president told me to grind off the sharp corner on the bottom (non cutting side) of the bevel. This is the most common cause of rings that won't take finish evenly. The bottom sharp corner burnished the wood so it is in affect crushed and won't accept the finish in the same way as the rest of the wood. You can't sand those darn rings out because it goes really deep when this happens.
After I sharpen my gouge I simply move the gouge so the grinder can knock off that sharp corner and hit it a quick lick. That usually does it.

 

Dry wood will generate more heat than wet wood. This is in part due to bevel rubbing and part of the friction of the cutting edge going through the wood. I have put blisters on my thumbs more than once from using a freshly sharpened card scraper (flat work only). Sharp tool is necessary. If the rings are on the inside only, that is from having a sharp edge on the bottom of the bevel on your gouge. Rounding it over really helps that out.

There is a big difference between riding the bevel and rubbing the bevel. This is a very 'touchy/feely' sensitive thing where you need to feel the tool very gently rubbing the bevel as a guide, not bearing down on the bevel to keep your tool in line. A well controlled cut, with a sharp tool requires almost no arm pressure. Another problem might be the 'white knuckle grip'. As said in an old Hollywood movie, master swordsman to the student, "Hold it like you would hold a bird. Too tight and you kill it. Too loose, and it flies away."

robo hippy

 

Thank you all for your suggestions. This streaking happens on the outside and is mostly visible in the endgrain areas. I'm not turning bowls but spherical confetti lamps. My gouge was freshly sharpened. I think I may apply to much force to rub the bevel, take off too much wood at a time and possibly have the lathe at too high an rpm. I'm not at the point where I have great control over what I'm doing and that may be the biggest issue.

I do have the impression that hard maple is very difficult to work with. Is that so or it is just that I need to practice more?

 

There is no substitute for practice. Reading forums and books and watching DVDs is good but you have to practice to develop basic tool control.

 

Hard woods in general are not a problems if you don't force the cut. You will be taking a much smaller bite with hard woods than you will with softer woods. If your tool is sharp and you cutting technique is correct even very hard woods cut easily it's just much much smaller shavings.

 

I'm going to say thinking BEFORE you watch, and rethinking AFTER. Analyze before you put your theories (or the author's) into practice. If you are cutting spheres (or other convex shapes) you are more vulnerable than ever to heel burnishing, the source of the compressed endgrain which is causing you fits. You have to concentrate on lifting the heel to provide clearance, because the shape wants to rub the heel you're not watching as you follow the edge.

Take smaller bites, as John says, not because the wood is hard, but because you have to keep a steep angle in order to avoid heel bruising. If the slope is less, you can widen up and let the tool be controlled more by the work. Depending on how much room you have to maneuver the tool, you may use a number of options.

Standard gouges here. Note the clearance angle on the lower set, and the tight twist on the shavings, resulting from the steep angle. http://i35.photobucket.com/albums/d160/GoodOnesGone/Roughing.jpg

Straight edges here. The first is what was called a beading tool before that appellation went to concave scrapers. The shavings are broader, though the tight twist only makes them look thicker. The broader shaving is a result of the tool being skewed to the direction of rotation. http://i35.photobucket.com/albums/d160/GoodOnesGone/Shoulder-Peeling.jpg

The final is a parting tool, and the shavings are paper thin, because there is almost no skew to the tool. So when you practice, lift the heel and watch the results. You're more likely to be able to avoid problems with the straight edge tools than the fat-bottomed gouge, though you could sacrifice some control and cut with a long side grind.

The demo is dry hard maple, and if you look at the pair of broad shavings to the upper right, you can see what happens on a larger diameter curve. Not tightly twisted, and thick at the leading, feathered on the trailing edge. That's the shaving you're looking for, broad or narrow - the one where the final cut sort of sneaks out of the wood.